Neurons release peptides that act as neuromodulators and participate in controlling a variety of behaviors. It is known that only a fraction of peptides packaged in large dense core granules is released in response to elevations in cytoplasmic [Ca2+]. Furthermore, this depletion of the releasable pool of granules typically requires trains of action potential and proceeds slowly. The cellular basis for the limited extent and rate of neuronal peptide secretion remains unknown. Recently, we demonstrated that expression of a preprohormone tagged with a variant of the Green Fluorescent Protein (GFP) enables study of the distribution and mobility of secretory granules in live growth cones of Nerve Growth Factor-treated PC12 cells. Surprisingly, confocal microscopy revealed that the releasable pool is not spatially defined. Rather, time lapse particle tracking and Fluorescence Recovery After Photobleaching (FRAP) suggest that peptide release is limited by the number of mobile granules and their slow rate of movement to docking sites in the plasma membrane. Here Total Internal Reflection Fluorescence Microscopy (TIRFM), an inducible GFP construct, and ratiometric calcium imaging are incorporated into our optical studies to explore how GFP-tagged secretory granules move to and dock on the piasma membrane of growth cones so that they can undergo exocytosis. Our goal is to determine whether calcium-evoked secretion and its facilitation by cAMP is governed by secretory granule dynamics.